Respirators (also referred to as "face masks" and "filtering face masks") are worn over the breathing passages of a person for two common purposes: (1) to prevent contaminants from entering the wearer's breathing track; and (2) to protect others from being exposed to pathogens and other contaminants exhaled by the wearer. In the first situation, the respirator is worn in an environment where the air contains substances harmful to the wearer, for example, in an auto body shop. In the second situation, the respirator is worn in an environment where there is a high risk of infection, for example, in an operating room.
To accomplish either of these purposes, the respirator must be able to maintain a snug leak-free fit to the wearer's face--otherwise, the wearer or persons in the vicinity of the wearer may be exposed to harmful contaminants.
For instance, the failure to obtain a leak-free fit when using a negative pressure respirator--i.e., a respirator that has a filter, and the wearer's lungs draw the air through the filter--allows air to enter or exit the interior of the respirator without passing through the filter media. Unfiltered air drawn into the respirator's interior can enter the wearer's breathing passage, and unfiltered exhaled air may expose others to contaminants exhaled by the wearer. In positive pressure respirators--i.e., respirators where uncontaminated oxygen or air is fed to the wearer from a pressurized vessel--an unsatisfactory fit not only exposes the wearer and others to contaminants, but it also is wasteful in that pure oxygen or air from the vessel can pass unused into the ambient environment.
Although there are many properly designed respirators that are very capable of achieving leak-free fits, wearers often encounter difficulties in determining whether or not a proper fit has been established. After donning the respirator, wearers frequently make adjustments in hopes of obtaining the proper fit, but without an accurate test they cannot determine for certain if they are safe. To put the wearer's mind at ease, investigators have developed a number of test procedures that are useful for determining whether leaks are present in both negative and positive pressure respirators.
Known test procedures may be classified as being qualitative or quantitative, and examples of each type are briefly described below.